parts whatever. A number of other ideas have been used for flush-tanks, such as a tank on trunnions, which tips when full and returns to its original position when empty, but experience seems to have demonstrated the inadvisability of any moving parts.

The outlet of the flush-tank should be at some elevation, the more the better, above the sewer. If no automatic appliance is used, the opening of the flush-tank may be in the bottom, stopped by a plug or cap, which is raised by an attached chain when the tank is full; or it may be in the side and be opened and closed by a valve, either sliding or hinged.

If water is led to the flush-tank by a pipe, this should be kept

below the effect of frost, turning and rising to a higher level inside the flush-tank if necessary.

Inlets are made with and without catch-basins (see Art. 20), and the openings are sometimes vertical (in the curb), sometimes horizontal (in the gutter), and sometimes inclined. Their

FIG. 486.-MILLER-MACKINTOSH FLUSHTANK AND MANHOLE.

By shutting off water and removing cap in rodding trough, sewer becomes accessible.

purpose being to admit water from the roadway to the sewer, the opening of each inlet should be sufficiently large to admit all the water which can reach it from the heaviest rain whose runoff the sewer is designed to carry. It may be so designed that the smaller of two openings, leading to a house sewer, shall pass the water from light rains or the first washings of a rain, while another larger one leads to a storm sewer. The opening should be at

the gutter where the water flows, and which should be slightly depressed at this point. If horizontal in the bottom of the gutter, one large opening is not permissible, but smaller ones, into which neither carriage-wheels nor feet of horses nor pedestrians can enter, must be used. The plate through which these holes are made must be able to support the most heavily loaded wheels that are likely to come upon it.

If the opening is through the face of the curb, in a plane either vertical or slightly inclined, it may be much larger. In some cases one large opening is used, entirely unprotected, through which children could and sometimes do fall. Except for this danger, such a clear waterway is an excellent arrangement. But it is advisable to so place one or more bars across the opening as to remove the danger referred to.

The total area of opening required may be found approximately by the hydraulic formulas for flow through horizontal or vertical orifices or over weirs, as the case may be. In the case of openings less than 3 inches across in any direction, an additional allowance should be made for the occasional stoppage of some of them by leaves, paper, etc. The vertical openings, being larger, are less liable to stoppage. If horizontal openings in the gutter are in the shape of slots, they should run across the line of the gutter. Large gutter inlets are preferable where the water approaches with considerable velocity. Otherwise the author prefers curb inlets.

Between the inlet opening and the sewer, the channel should be straight or have as easy bends as possible, that the run-off may have an uninterrupted flow. The use of a catch-basin greatly interferes with this, the water seething and whirling in it during storms; consequently the channel connecting it with the sewer should be larger than if a simple inlet were used. In some instances a pipe leads directly from the opening to the sewer, either with or without a water-seal trap. It is better, however, to obtain a more substantial structure by setting under the opening a small basin with a curved bottom from which the pipe leads directly to the sewer. There is much room for improvement in the designing of inlets, with a view to reducing to a minimum the head lost in passing through them. The channel, from inlet opening to connection pipe, should contain no offsets or abrupt changes in size or shape, as few bends as possible, and these with long radii. Where the opening is horizontal, the basin is desirable to support the weight which may come upon the grating and, where a trap is used, to enable it to be placed below danger of freezing. It also facilitates inspection and cleaning of the connection-pipe.

A catch-basin usually consists of a well under the inletopening and below the connection-pipe to catch the heavier matters. It is sometimes placed between the inlet and the sewer on the line of the connection-pipe, and sometimes at the sewer in connection with a manhole. To be at all effective it should extend more than 18 inches below the connection-pipe, since a heavy rain will keep the water in it so stirred up as to wash out any deposits above that point. The bottom of the catch-basin should be covered with a flag-stone or the most substantial of concrete to receive the impact of the water, and be smooth to make cleaning easy,

Inlet and catch-basin wells may be built of concrete or of stone, but are usually of brick. Catch-basin wells are usually watertight, that water may constantly cover the contents and lessen their odors. An objection to this is the possibility that mosquitoes will breed in the water. (This may be prevented by pouring a little oil into each basin after every rain.) Some